Manifold for heat exchanger and process therefor

ABSTRACT

Manifold for a heat exchanger intended to be joined by brazing or soldering to heat transfer tubes. A portion of a surface of the manifold that will be joined to the tubes is proved with at least one recess in which a brazing material is mechanically locked.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of International Application No.PCT/EP99/09144, filed Nov. 22, 1999, and European Patent Application No.99200246.9, filed Jan. 29, 1999.

BACKGROUND OF THE INVENTION

This invention relates to an aluminium product to be joined by brazingor soldering to another aluminium product.

Such a product is generally known in WO-A-98/51983 and all technicalinformation disclosed is that patent application is incorporated byreference in this description.

It is common practice to join aluminium components by disposing analuminium brazing alloy between or adjacent to the component surfaces tobe joined, and heating the brazing alloy and the joining surfaces inappropriately assembled fashion to a temperature (brazing temperature)at which the brazing alloy melts while the components remain unmelted.Upon subsequent cooling the brazing alloy forms a filet or joint thatbonds the joining surfaces of the components. For assured selectivemelting of only the brazing alloy in the heating step, it is commonlypreferred that the melting point of the brazing alloy be at least 30° to40° C. lower than that of the metal of the components. An example of atypical aluminium brazing alloy is an aluminium-silicon eutecticcomposition, which starts to melt at about 577° C.

The use of clad composite aluminium brazing sheet to join aluminiumalloy components is well known. Brazing sheet is used to manufactureheat exchanger components such as tubes, fins, headers, tanks, flowdividers, etc. However an important limitation is that it is difficultto manufacture complicated profiles only using rolled sheet. Forcomplicated profiles such as e.g manifolds or micro tubes, the extrusionprocess may offer a more cost efficient and better quality solution. Onedisadvantage of using extruded profiles is has been a problem furnishingextrusions with a braze alloy coating.

The CD process is one of the methods that have been developed in orderto produce a braze “clad” extruded profile. In this process the profileis coated with AlSi particles coated with NOCOLOK flux Adhesion of thecoating is achieved through the use of a binder (polymer). The additionof AlSi particles provides filler metal for braze joints during thebrazing process.

In the “Brazeliner” process the profile is coated with a mixture ofNOCOLOK and particulate AlSi-alloy. Adhesion of the coating is achievedthrough the use of a binder@x (polymer). The AlSi particles melt andflow during brazing.

The Sil flux process is a method where the profile is coated with amixture of NOCOLOK and fine Silicon particles. Adhesion of the coatingis achieved through the use of a binder. (polymer). During brazing theSi diffuses into the surface and forms a eutectic AlSi alloy thuscreating filler metal for braze joints “in situ”.

A disadvantage with all the above processes is the use of a binder. Thebinder tends to “poison” the furnace atmosphere and also presents anenvironmental issue. In order to overcome these problems costly furnacemodifications have been required. For the Sil-Flux process also Siliconerosion tends to be more pronounced due to the presence of particulateSilicon.

Arc flame spray coating is another method where the profile is coatedwith an AlSi alloy. During this process a lot of oxides is introducedthat is undesirable in the brazing/soldering operation.

With all the above efforts to produce an extruded product with apre-placed filler metal, it still remains a problem in the industry.

BRIEF SUMMARY OF THE INVENTION

It is therefor an object of the invention to provide an aluminiumproduct in which the above mentioned problems are avoided.

This object is achieved in that the position of the outer surface of thefirst aluminium product which will be connected to the second aluminiumproduct is provided with at least one recess in which there is locked anamount of brazing material.

By means of this “mechanical” assembly it is possible to provide analuminium product in an integrated manner with the amount of brazingmaterial without the need to use special compositions in order to adherethe brazing material to the aluminium product. It becomes even possibleto use commercially available brazing materials, which after beinglocked in the recess allow the aluminium product to be handled in anormal way, such that the brazing material stays in place duringsubsequent handling or fabrication operations such are shipping,machining, forming, stamping, cutting, washing or degreasing.

In a preferred embodiment of the invention each recess has the shape ofa groove and the amount of brazing material has the shape of a wire.

In this way it becomes possible to use commercially available flux corewire thus eliminating the need for additional fluxing of the aluminiumproduct.

Other advantages and characteristics of this invention will become clearfrom the following description, reference being made to the annexeddrawings, in which

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a manifold as an aluminium productaccording to the invention,

FIG. 2 is a cross-section of a manifold as an aluminium productaccording to the invention showing different shapes of grooves,

FIGS. 3A-3C are schematic cross-sections of a modified embodiment of amanifold according to the invention,

FIGS. 4A-4C are schematic cross-sections of another modified embodimentof a manifold according to the invention, and

FIG. 5 is a cross-section of a third modified embodiment of a manifoldaccording to the invention,

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, there is shown by way of example a manifold 1, but theinvention is not restricted to this type of products, but can be used inany aluminium products which must be brazed after shaping.

The manifold 1 is made up of aluminum tubes 3 with holes (not shown) foraccommodating the ends of heat transfer tubes. As further shown in FIG.1 the manifold 1 consists of a number of parallel tubes 3, with commonwall portions 6, and shaped as a flat product having two bigger walls 4and 5. In the wall 4 and parallel to the flowing channels of the tubes 3a number of grooves 8 is provided, which are located above eachintermediate wall section 6 of the manifold 1. In the embodiment shownthese grooves 8 have a more than half circular cross-section. Themanifold 1 shown in FIG. 1 can conveniently be made by means of anextrusion.

As shown in the left end portion of FIG. 1 a brazing wire can beinserted into the groove 8 in such a way that it is fixed by aform-locking manner in the groove. When later in the manufacturing ofthe heat exchanger the manifold 1 has to be connected with the endportions of the heat exchanging tubes, the material of the wires 9 canbe melted and used as brazing material.

In the right end portion of FIG. 2 there is shown a different type ofgroove 8B having a cross-section in the shape of a trapezium. It ispossible to have a round brazing wire clamped into such a groove, butalso brazing wires with other cross-sections can be clamped such assquare, triangular or oval.

The grooves 8, 8B may be designed in such a way that the brazing wirecan be positioned on top of the groove and subsequently be mechanicallyinserted and locked in the groove, e.g. by applying a pressure. This canbe done immediately after extrusion of the manifold, but also later inthe manufacturing of the manifold or even just before the production ofthe heat exchangers.

The different steps in the process of preparing such a manifold may be

cutting the extruded profile into pieces of a defined length;

fabricating holes in the profile by e.g. stamping, milling, sawing,etc.;

inserting flow dividers into the profile pieces;

washing an degreasing of the profile pieces;

inserting the brazing wires;

inserting the heat exchanger tube ends into the holes made in theprofile pieces;

brazing the tube ends to the manifold or profile pieces.

During the brazing/soldering process the brazing wire melts and throughcapillary action and if present assisted by a flux, the molten wire isdrawn into the manifold/tube joint. During cooling the liquid metalsolidifies to create a solid joint between manifold and tubes and othercomponents that are attached to the manifold in such a way that it is incontact or dose to the brazing wire.

Profiles such as manifolds for heat exchangers are generally made eitheras extrusions or from clad composite braze sheet. It is common toproduce manifolds from a variety of aluminium alloys, examples being theAA 1000 or 3000, and more particularly AA 1100, AA 1197, AA 3003 and AA3102. Also it is common that the filler metal used to join the manifoldto the tubes and other components are from the AA 4000 series aluminiumalloys or more particularly AA 4343, AA 4045, AA 4047, AA 4343+1% Zinc,and AA 4045+1% Zinc AA is common alloy designations by the AluminiumAssociation (AA). Those skilled in the art will recognise that theteachings of this invention are not limited to the particular aluminiumalloys used by example in the following description, but can generallybe considered to encompass a wide variety of aluminium base alloys.

The shape of the groove is important in that it must be designed in sucha way that

a. the filler wire is “locked” in place,

b. it protects the filler wire from being tom out or in other waysdamaged during product handling.

c. the cross sectional area is sufficiently large for the groove tocarry enough filler metal for successful brazing or soldering.

In the FIGS. 3A-3C there is shown another embodiment of a manifoldaccording to the invention. As shown in FIG. 3A the manifold 10 isprovided with a trapezium-shaped groove 11, which is designed such thatwhen pressure is applied to a filler metal wire 12 which is placed inthe groove (FIG. 3B), this wire 12 is squeezed into the groove andmechanically locked in place. This wire 12 can if needed be pressed inplace by passing the manifold 10 through the nip of a set of pressingrolls, thereby obtaining a final shape as shown in FIG. 3C.

The embodiment of FIGS. 4A-4C is somewhat different form the one shownin the FIGS. 3A-3C in that the manifold 15 is provided with a groove 16with a upper cross-dimension which is larger than the diameter of thefiller metal wire 17 to be placed in said groove (FIG. 4B) In this waythe wire 17 can easily be positioned into the groove 16 whereupon themanifold 15 can be passed through the nip of a set of pressure rollsthereby obtaining the product as shown in FIG. 4C.

In FIG. 5 there is shown a manifold 20 which is modified with respect tothe manifolds shown in the previous drawings in that here a round tubeis used as manifold, which is provided with two extensions 21 and 26providing channels 23 and 24, which are located at the ends of theopenings 25 to be made in the manifolds for accepting the heatexchanging tubes.

In each case the extruded tube has channels 23, 24 placed in such a wayas to allow the brazing compound or filler 27 wire to nearly contact thetube that is eventually fitted into the opening or slot 25. When thebrazing compound reaches its melting point the liquid metal can be moreeasily drawn to the joint by capillary action. When the pipe diameter isrelatively small, e.g. 10-40 mm, the radius of currature is such thatthe major force moving the molten filler metal to the joint iscapillary. The typical orientation of a heat exchanger in a brazefurnace is with the long axis of the manifold pipe in the horizontaldirection. The joints will be drawing metal from both the top and bottomchannels.

As the diameter becomes larger the effect of gravity becomes moreimportant. In this case the design of the manifolds can be modified insuch a way that the openings or slots 15 are made in a surface ofminimal currature to prevent the filler metal from sogging and fallingout of the channel when molten.

The present invention also offers a method of closely controlling theamount of filler metal. Those skilled in the art will know that toolittle filler metal will result in small or non leak proof fillets, andthat too much can result in tube erosion which in the worst case alsowill end up as leaks. The required amount of filler metal for successfulbrazing or soldering is dependent on the actual void or gap to befilled. In the case of a manifold to tube joint/fillet in a heatexchanger, the volume of this void will vary with the outer dimensionsof the tube, the inner dimensions of the manifold slot (where the tubeis inserted) and the wall thickness of the manifold. When the totalnumber of manifold to tube joint per manifold is known, the total amountof filler metal required can be calculated. Based upon the result ofthis calculation the required filler metal can be easily dosed into thegrooves.

What is claimed is:
 1. A first aluminum article having a surfaceconfigured for joining by brazing or soldering to a second aluminumarticle, a portion of the surface of the first aluminum article beingprovided with at least one recess in which an amount of brazing materialis mechanically locked as a result of cross-sectional shapes of thebrazing material and the recess.
 2. A first aluminum article accordingto claim 1, wherein the recess has the cross-sectional shape of a grooveand the amount of brazing material has the cross-sectional shape of awire.
 3. A first aluminum article according to claim 1, wherein theamount of brazing material is mechanically locked in the recess by meansof force-transmitting or form-locking manner.
 4. A first aluminumarticle according to claim 2, wherein the groove has a circularcross-section of more than half a circle.
 5. A first aluminum articleaccording to claim 2, wherein the groove has a trapezium cross-sectionwith a smaller width defining an opening to the groove than a widthdefining the base of the trapezium at the bottom of the groove.
 6. Afirst aluminum article according to claim 4, wherein the brazing wire ismechanically locked within the groove by a deformed portion of thegroove.
 7. A first aluminum article according to claim 1, wherein thefirst aluminum article is an extrusion and the recess extends in adirection parallel to an extrusion direction of the first aluminumarticle.
 8. A first aluminum article according to claim 1, wherein thefirst aluminum article is a manifold for a heat exchanger.
 9. A processof producing a first aluminum article having a surface configured forjoining by brazing or soldering to a second aluminum article, wherein aportion of the surface of the first aluminum article is provided with atleast one recess in which there is mechanically locked an amount ofbrazing material, the process comprising extruding the first aluminumarticle to form the recess as at least one groove extending along theextrusion direction, and then mechanically locking the amount of brazingmaterial in the form of a brazing wire inserted into the groove.
 10. Aprocess according to claim 9, wherein the brazing wire is mechanicallylocked in the groove by deforming a portion of the groove.
 11. A processaccording to claim 9, wherein the brazing wire is mechanically locked inthe groove as a result of the brazing wire having a differentcross-sectional shape than the groove.
 12. A process according to claim9, further comprising the steps of assembling the second aluminumarticle with the first aluminum article, and then brazing the first andsecond aluminum articles together by heating the first and secondaluminum articles to melt and flow the brazing wire.
 13. A heatexchanger comprising a manifold having a surface configured forreceiving tubes to which the manifold is to be joining by brazing orsoldering, the surface of the manifold comprising at least one groove inwhich a brazing wire is mechanically locked as a result ofcross-sectional shapes of the brazing wire and the groove.
 14. A heatexchanger according to claim 13, wherein the brazing wire ismechanically locked in the groove by a deformed portion of the groove.15. A heat exchanger according to claim 13, wherein the brazing wire ismechanically locked in the groove as a result of the brazing wire havinga different cross-sectional shape than the groove.
 16. A heat exchangeraccording to claim 13, wherein the groove has a circular cross-sectionof more than half a circle.
 17. A heat exchanger according to claim 16,wherein the brazing wire is mechanically locked within the groove by adeformed portion of the groove.
 18. A heat exchanger according to claim13, wherein the groove has a trapezium cross-section with a smallerwidth defining an opening to the groove than a width defining the baseof the trapezium at the bottom of the groove.
 19. A heat exchangeraccording to claim 18, wherein the brazing wire is mechanically lockedin the groove as a result of the brazing wire having a differentcross-sectional shape than the groove.
 20. A heat exchanger according toclaim 13, wherein the manifold is an extrusion and the groove extends ina direction parallel to an extrusion direction of the manifold.